The subject matter disclosed herein relates in general to hold down and release mechanisms (“HDRMs”) for use, for example, on satellites, and in particular to an HDRM that contains an integral sensing device which senses a parameter of interest, such as the amount of an applied tensile preload to the HDRM, and communicates the parameter of interest to a control device.
Launch vehicles typically have multiple stages and are used to carry payloads during travel away from the Earth's surface after the vehicles are launched, and then place or deploy the payloads into orbit or beyond. These payloads are commonly referred to as satellites if they are intended to orbit a body (e.g., Earth) after deployment, or as spacecraft if they are intended to leave the Earth's orbit after deployment. Sometimes the terms “satellites” and “spacecraft” are used interchangeably.
Spacecraft typically utilize hold down and release mechanisms (“HDRMs”) (i.e., a “hold-then-separate” device) to securely hold, retain or stow elements of the spacecraft during launch and also during ground transport of the spacecraft to the launch site. These elements, such as solar arrays, antenna reflectors, radiators, instrument booms, propulsion pointing actuators, doors, sensors, etc., are deployed as desired by activating the HDRMs.
An HDRM is generally an electro-mechanical, “one-shot” device in that after it is activated to release its stowed or held element, the HDRM either needs to be replaced, refurbished, or reset—depending on the type of technology that the HDRM employs. An HDRM is typically not a motorized device or other type of device that will return to its original state without some type of external intervention.
HDRMs are generally broadly categorized into three different types: explosive, pyrotechnic, and non-explosive—depending upon the type of activation or actuation mechanism utilized. Explosive and pyrotechnic HDRMs are also both typically referred to as energetic HDRMs, while a non-explosive HDRM or a non-pyrotechnic HDRM is also typically referred to as a non-energetic HDRM. An explosive HDRM is one whose activation mechanism detonates on command, while a pyrotechnic HDRM is one whose activation mechanism burns or deflagrates on command. A non-energetic HDRM is one that typically utilizes an activation mechanism such as a fuse wire or link wire that heats and weakens on command from a control unit when an amount of electrical current passes through the wire, thereby causing it to melt and break. Other types of non-energetic HDRMs utilize a shape memory alloy or utilize the volumetric expansion of certain materials, such as paraffin, when changing from solid to liquid phase. For simplicity, the discussion herein will focus on the fuse wire or link wire style of non-energetic HDRM. However, it can be seen that embodiments of the present invention described herein would be applicable to all types of non-energetic and/or energetic HDRMs.
In a particular type of non-energetic HDRM, when the fuse wire breaks, a release wire that is wrapped around and thereby enclosing the two parts or halves of a cylindrical split spool assembly is released, thereby releasing for movement a pre-loaded device (e.g., a bolt or release pin) attached to the split spool assembly. Release of the bolt or pin subsequently releases a stowed element of the spacecraft. This type of non-energetic HDRM is commonly referred to as a split spool release device (“SSRD”). Other common types of non-energetic HDRMs are commercially available.
In the relevant art, a relatively broad combination of a control unit, a plurality of non-energetic and/or energetic devices, and an interface bus through which signals (e.g., power and data) are sent and received as between the control unit or controller and the non-energetic and/or energetic devices (i.e., two-way communication) is generally referred to as a “networked initiation system.” It is a distributed type architecture in which the various components (e.g., the control unit and the non-energetic and/or energetic devices) are located at different places on the launch vehicle or spacecraft and are all connected together by the interface bus.
Also in the relevant art it is known that the various elements (e.g., solar arrays, antenna reflectors, radiators, instrument booms, propulsion pointing actuators, doors, sensors, etc.) that are held, restrained or stowed with respect to the satellite during launch using HDRMs are held or fastened to the satellite prior to launch at desired tensile preload values. The desired tensile preload values are typically applied manually by torqueing a nut or a bolt or some other type of hold down device associated with the HDRM. A typical launch vehicle or spacecraft application may have 50 or more locations where at each location a nut, bolt or some other hold down device is manually torqued to a value that is sufficient to securely hold the various elements in place during launch.
While preload may be applied through torqueing of a nut or bolt, the torque value typically does not provide a direct measurement of the applied tensile preload. Instead, it is common to use an instrumented bolt or a strain gauge together with external test or measuring equipment to measure the amount of the applied tensile preload. The strain gauges are often temporarily secured to the HDRMs. Then, after the satellite has been transported on the ground to the launch site, the strain gauges and test equipment are used again to check the amount of applied tensile preload to ensure that the amount of preload has not changed during travel to the launch site. Once the amount of applied tensile preload has been verified at the launch site, the strain gauges (or at least the wires protruding therefrom) are then removed. Removal of the strain gauge wires introduces the risk of damage to the spacecraft. Also, sometimes HDRMs are inaccessible once the satellite is assembled. Thus, the ability to measure the applied tensile preload may be impossible due to the lack of accessibility to the buried HDRMs. As can be seen from the foregoing, this entire manual measuring process can be a time consuming procedure with inherent risk.
The discussion above is specific to measurement of preload of an HDRM but is can be seen that the ability of an HDRM to measure other parameters, such as temperature, may also have similar advantages.
What is needed is an HDRM that contains an integral sensing device which senses a parameter of interest, such as the amount of an applied tensile preload to the HDRM, and communicates the amount of the sensed tensile preload to a control device for use thereby.